Question

if 3a-7b=10 and ab=-1, find the value of 9a^2 + 49b^2

Answer 1

we know that,
3a-7b=10
squaring both sides
(3a-7b)^2=10^2
(3a)^2-2*3a*7b+(7b)^2=100
ab=-1
9a^2+42+49b^2=100
9a^2+49b^2=100-42
9a^2+49b^2=58