If (7x - 10y) = 8 and xy = 5, then what is the value of $49x^2 +100y^2$?
Answer & explanation
Correct answer: option 1
(7x - 10y) = 8 and xy = 5
We know that,
(a - b)2 = a2 + b2 - 2ab
= (7x - 10y)2 = 82
= 49x2 + 100y2 - 2 × 7x × 10y = 64
= 49x2 + 100y2 - 140xy = 64
= 49x2 + 100y2 = 64 + 140xy
= 49x2 + 100y2 = 64 + 140 × 5
= 49x2 + 100y2 = 764