Question

if x - y = 4 and xy= 21 find (x+y)²​

Answer 1

Step-by-step explanation:

$givn \: x - y = 4 \\ and \: xy = 21 \\ now \\ clearly \: x = 7 \\ and \: y = 3 \\ {(x + y)}^{2} = {(7 + 3)}^{2} = {10}^{2} = 100$

2nd method

${(x + y)}^{2} = {(x - y)}^{2} + 4xy \\ = {4}^{2} + 4 \times 21 \\ = 16 + 84 \\ = 100$