Question

if a2 + b2 =9 find the value of 3 (a+b)2 - 2(a-b)2

Answer 1

${a}^{2} + {b}^{2} = 9 \\ 3( {a + b) }^{2} - 2( {a - b})^{2} = \\ 3 {a}^{2}+3 {b}^{2}+6ab-2 {a}^{2} -2 {b}^{2}+4ab \\ = {a}^{2} + {b}^{2} + 10ab \\ = 9 + 10ab$