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If x + y = 17 and x – y = 5, what is the value of xy?
A. 6
B. 11
C. 17
D. 66
E. 90
A. 6
B. 11
C. 17
D. 66
E. 90
04 Jan 2022, 08:17
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Bunuel
If x + y = 17 and x – y = 5, what is the value of xy?
A. 6
B. 11
C. 17
D. 66
E. 90
Formula: \((\frac{a+b}{2})^2-(\frac{a-b}{2})^2\)A. 6
B. 11
C. 17
D. 66
E. 90
= \((\frac{17}{2})^2-(\frac{5}{2})^2\)
= \(\frac{289}{4}-\frac{25}{4}\)
= \(66\)
06 Jan 2022, 19:10
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Seems rather onerous to follow the method above. My suggestion would be the combination method.
(x + y = 17) - (x - y = 5) => 2y = 12 => x=6 => x + 6 = 17 => x = 11 => (6)(11) = 66.
(x + y = 17) - (x - y = 5) => 2y = 12 => x=6 => x + 6 = 17 => x = 11 => (6)(11) = 66.
