Question

14. If 3x + 4y = 16 and xy = 4; find the value of
9xsq + 16y sq
​

Answer 1

3x + 4 y= 16

squaring

9x^2 + 16 y^2 + 2(3x)(4y)= 256

9 x^2 + 16 y^2 + 24 xy = 256

As xy= 4

9 x^2 + 16 y^2 +24(4)= 256

9 x^2 + 16 y^2 + 96 = 256

9 x^2 + 16 x^2= 256 -96 = 160