Question

if 3x+4y=13 and xy=1 find 3x-4y

its from expansion

Answer 1

Answer:

1

Step-by-step explanation:

3x + 4y = 13

Squaring both Sides

$9x^{2} + 16x^{2} + 24xy = 169$

Substract 48xy from both sides, we get

$9x^{2} + 16x^{2} - 24xy = 169 - 48xy$

Given xy = 1

$9x^{2} + 16x^{2} - 24xy = 169 - 48$  

$9x^{2} + 16x^{2} - 24xy = 121$

Using $a^{2} + b^{2} + 2ab = (a+b)^{2}$

3x - 4y = 11