Advanced MathVery hardSquare of a sum from the sum of squares and the product
Advanced Math practice question
If p² + q² = 58 and pq = 21, what is the value of (p + q)²?
Answer: 100
(p + q)² = p² + 2pq + q² = (p² + q²) + 2pq = 58 + 42 = 100.
Common wrong answers
- If you answered 16
- 16 is (p − q)² = 58 − 42, the square of the DIFFERENCE.
- If you answered 37
- 37 subtracts (58 − 21); (p + q)² adds the cross term.
- If you answered 79
- 79 adds pq once (58 + 21); the expansion has 2pq.
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