alleryFind the value of x² + y² if x + y = 10 and xy = 21:
A48
B58
C79
D100
Answer & Solution
Correct answer: B. 58
Use the identity (x + y)² = x² + 2xy + y².
We have **So x² + y² = (x + y)² − 2xy.
That is **So x² + y² = 10² − 2·21.
That is **So x² + y² = 100 − 42.
So **So x² + y² = 58.**.
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