Question

If a + b = 9 and a2+ b2= 61, then ab is

A) 20 B) 10 C) 81 D) 142

Answer 1

Answer:

20

Step-by-step explanation:

a+b=9 ,a²+b²=61

so,

(9)²=61+2ab

81-61=2ab

20=2ab

20/2=ab

10=ab

Answer 2

Step-by-step explanation:

a+b=9

=>(a+b)2=9×9=81 but a2+b2=61

=>a2+b2+2ab=81

=>2ab=81-61=20