Question

find the value of x^3+y^3 when x+y = -4 and xy= 5

Answer 1

Answer:

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Step-by-step explanation:

so here x+y=-4

so squaring both sides

we get

x square+y square+2xy=16

since xy=5

we get x square+y square+(2×5)=16

=16-10

=6

so thus then

here x cube+y cube is in form a cube+b cube

so we know that

a cube+b cube=(a+b)(a square+b square-ab)

thus accordingly we get

x^3+y^3=(x+y)(x square+y square-xy)

=(-4)(6-5)

=-4×1

=-4

hence final answer is -4