Question

IF
$a + b = 5 and \: a{}^{2} + b {}^{2} = 13. \: find \: ab$
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Answer 1

Step-by-step explanation:

a+b = 5

squaring both side

( a+b) ²=5²

a²+ b²+ 2ab = 25

a²+b²=25-2ab

but it is given that a²+b²= 13 .So, putting this value

13=25-2ab

13-25=2 ab

-12=2ab

-6= ab