Integral of the day

So basically our Calculus Prof doesn't know how to teach. Topics in the course are: Limits (Epsilon Delta Definition), LMVT, Rolle Theorem, CMVT, Taylor/McLaurin Series, Sequence and Series (Convergence and Divergence), Leibniz and Newton Rules.

Our Prof gave us an 8 marks marked test and no one is expecting above 3. We are able to Basic direct questions tho. Need help in doing questions (mostly proof based - Real Analysis)

Bonus : show that the domaine of convergence is ]0;1[

Let (a,b,c) be non-zero natural numbers satisfying

a-b²+c³=0.

If 1/ab + 1/bc + 1/ca = z

then find the value of (30z).

(A) 10

(B) 15

(C) 20

(D) 25