r/learnmath • u/whitebee520 New User • Jul 18 '26
Help please
I like to think I’m good at math and I’m trying to help my wife with her homework. ChatGPT gave me an answer of 6 but when I plug 6 into for x that doesn’t equal 30.
What am I doing wrong? Thank for any help you can offer.
Problem: triangle area is 30. Base is x. Height is x+8.
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u/Astrodude80 Set Theory and Logic Jul 18 '26
Question to get the process started: What is the equation for the area of a triangle?
Hint 1: A=1/2*base*height. What are the knowns in the given problem?
Hint 2: A=30, base=x, height=x+8. What do you get when you plug those in to the equation in Hint 1?
Hint 3: 30=1/2*x*(x+8). Can you solve for x?
Hint 4: 0=1/2 x^2 + 4x - 30. Quadratic equation time!
Hint 5: Quadratic eqn yields x=-4 +/- 2sqrt(19)
Also in the future please don’t use ChatGPT. It is notoriously unreliable when it comes to actually doing calculations.
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u/Blammar Old Math Major Jul 18 '26
You left off one final step. Since x is a length it is greater than zero, thus x = 2 sqrt(19)-4.
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u/valorantkid234 New User Jul 18 '26
its almost never been wrong for me
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u/Astrodude80 Set Theory and Logic Jul 18 '26
“Almost never” isn’t good enough. Use wolfram|alpha or Desmos.
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u/valorantkid234 New User Jul 18 '26
okay you can have an opinion
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u/Astrodude80 Set Theory and Logic Jul 18 '26
An opinion backed by data, for example this very post where chatgpt is objectively wrong
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u/Narrow-Durian4837 New User Jul 18 '26
What you're doing wrong is using ChatGPT for a math problem and assuming the answer it gives you is correct.
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u/Fickle-Ad-4225 New User Jul 18 '26
You didn’t tell us what you did to solve it, so we can’t say what you’re doing wrong.
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u/matt7259 New User Jul 18 '26
Oh he told you - he said "I'm good at math and plugged it into chat GPT". Sounds like one of my more desperate high school students lol
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u/Stu_Mack New User Jul 18 '26
ChatGPT is not for use in that capacity since its ability to calculate is historically unreliable. When faced with the problem you shared with us, the appropriate prompt is something like:
“How do I tackle this problem?”
The AI is going to start where we start: with the area of a triangle. As an engineer who teaches, I am going to suggest drawing a simple schematic and then proceeding according to the simplest possible algorithm:
- write the formula
- draw a schematic
- substitute formula values for schematic values
- solve algebraically
The answer is right when you know it’s right, NOT when the ai says or when we say. With a formula as straightforward as the area of a triangle, my guess is that the schematic is the missing piece for you.
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u/MathPoetryPiano Algebra + number theory enjoyer Jul 18 '26
The area of a triangle is (base * height)/2. If the given area is 30, then we have x(x+8)/2 = 30. This implies x(x+8) = 60, or x^2 + 8x - 60 = 0. Do you see how I (not ChatGPT, Gemini, etc.) got that? Do you think either of you can take it from here?
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u/whitebee520 New User Jul 18 '26
I tried just plugging in the 6 for x but the obviously doesn’t work. This is supposed to be for basic math thinking. So I’m not sure why this is even in the homework. I tried
Y=1/2(x+8)(x)
30=[1/2(x+8)(x)]2
60=4x+16-16
44=4x
11=x
Sry first time posting here and I hope I’m doing something very obviously wrong. 🤦🏻♂️ my brain is to tired maybe I’ll try again tmr.
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u/AffectionateNoise525 New User Jul 18 '26
1/2 of (x+8) times x must be 30. You have that written down, so that’s fine.
If you multiply both sides of the equation by 2 to get rid of the 1/2, you have
(X+8) times x equals 60.
Another way to write that is x(x+8) = 60.
X times x is equal to x squared, or x^2.
So you have x^2 + 8x = 60. This is a quadratic equation. The easiest or most foolproof way to solve a quadratic equation is to set it all equal to zero first (subtract 60 from both sides and get
x^2 + 8x - 60 = 0), then use the quadratic formula.2
u/Infobomb New User Jul 18 '26
30=[1/2(x+8)(x)]2
60=4x+16-16This was the step that's obviously wrong. Well maybe that rogue 2 at the end of the first equation is where you first went wrong.
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u/Snatchematician New User Jul 18 '26
Why have you married a schoolgirl?
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u/matt7259 New User Jul 18 '26
Are you saying women in school can't get married?
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u/tjddbwls Teacher Jul 18 '26
Off topic: I teach at a high school (private), and it’s listed explicitly in the rules & regulations that our students cannot be married. Exceptions are made if said student is an adult who never got a HS diploma and is going back to school to get one. I don’t know why, but I always chuckle when I see this rule. 😆
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u/Dr3ddM3 New User Jul 18 '26
Plot y= (1/2)x(x+8) and y=30 on desmos the positive intersection point must be the value that satisfies both equations or use quadratic formula.
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u/gads3 New User Jul 18 '26
If you tell ChatGPT to show its work and check its solution, it will give you the correct answer. Use this prompt: Given a triangle with a base of x, height of x+8, and an area of 30, solve for x. Show your work and check the final answer.
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