if 3x +4y =16 and 3x - 4y=4,find the value of xy [Hints:Use the formula(p+q)2-(p-q)2=4pq]?
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3x+4y=16
squaring both side
(3x+4y)²=256 -----(1)
also
3x-4y=4
squaring both side
(3x-4y)²=16.------(2)
subtracting equation (1) from (2)
(3x+4y)²-(3x-4y)²=256-16
we know that (p+q)²-(p-q)²=4pq
4×3x×4y=240
48xy=240
xy=240÷48=5
so xy=5
squaring both side
(3x+4y)²=256 -----(1)
also
3x-4y=4
squaring both side
(3x-4y)²=16.------(2)
subtracting equation (1) from (2)
(3x+4y)²-(3x-4y)²=256-16
we know that (p+q)²-(p-q)²=4pq
4×3x×4y=240
48xy=240
xy=240÷48=5
so xy=5
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if x^2+y^2=26 and xy=3,find value for x+y
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