Question
If $a^2+ b^2= 34$ and $ab = 12;$ find$ : 7(a - b)^2- 2(a + b)^2$
✓
Answer
$a^2+b^2= 34,ab= 12$
$(a+b)^2=a^2+b^2+2ab$
$= 34 + 2 \times 12 = 34 + 24 = 58$
$(a-b)^2=a^2+b^2-2ab$
$= 34 - 2 x 12 = 34- 24 = 10$
$7(a-b)^2-2(a+b)^2= 7 \times 10 - 2 \times 58 = 70 - 116 = - 46$
$(a+b)^2=a^2+b^2+2ab$
$= 34 + 2 \times 12 = 34 + 24 = 58$
$(a-b)^2=a^2+b^2-2ab$
$= 34 - 2 x 12 = 34- 24 = 10$
$7(a-b)^2-2(a+b)^2= 7 \times 10 - 2 \times 58 = 70 - 116 = - 46$
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