Question

3x- 7y =10 and xy= -1 find the value of 9xsquare + 49ysquare

Answer 1

3x-7y=10
3×(-1)-(7×-1)=10
-3x-7y=10
10xy=10
xy =10/10
xy=1
(9x)2+(49y)2
81x+2401y
=2482xy
2482×1
=2482

Answer 2

Squaring on both sides,

=(3x-7y)^2=10^2

=(3x)^2-2X3xX7y+(7y)^2=100

=9x^2-42xy+49y^2=100

=9x^2-42(-1)+49y^2=100 [substituting xy= -1]

=9x^2+42+49y^2=100

=9x^2+49y^2=100-42=58