If x-y=4and xy=21 find yhe value of x^3-y^3
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solution:-【 hope helps 】
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solution:-【 hope helps 】
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x=4-y
x=21/y
we can write from both equation
21/y=4-y
4y-y²-21=0
y²-4y+21=0
y²-7y+3y+21=0
(y-7)(y+3)=0
so the y=7 or -3
now either x is 3 or -7
now x³-y³= 27-343=-316
or, x³-y³= -27+343= 316
x=21/y
we can write from both equation
21/y=4-y
4y-y²-21=0
y²-4y+21=0
y²-7y+3y+21=0
(y-7)(y+3)=0
so the y=7 or -3
now either x is 3 or -7
now x³-y³= 27-343=-316
or, x³-y³= -27+343= 316
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