Question

If x+y=7,then find the value of x³+y³+27+21xy​

Answer 1

Answer:

$x + y = 7 \\ y = 7 - x \\ {x}^{3} + {y}^{3} + 27 + 21xy \\ {x}^{3} + (7 - x)^{2} + 27 + 21x(7 - x) \\ {x}^{3} + 49 - 14x + {x}^{2} + 27 + 147x - 21 { x}^{2} \\ {x}^{3} - 20 {x}^{2} + 133x + 7 6$

$\blue{hope it helps you}$

Answer 2

Finding the value:

Step-by-step explanation:

$\ Given \ value: \\\\\ x\ +\ y\ = 7\\\\\ find: \\\\\ x^3\ +\ y^3 \ +\ 27 \ + \ 21 \ xy ....................(i)\\\\\ Solution: \\\\\ x\ +\ y \ = 7\\\\\ x\ = \ 7\ - y\\\\\ put \ the \ value \ x \ in \ equation \ (i) \\\\\rightarrow \ (7-y)^3\ +\ y^3 \ +\ 27 \ + \ 21 \ (7-y)y \\\\\ formula: \\\\(a-b)^3 =\ a^3 - b^3 -3a^2b+3ab^2 \\\\\rightarrow \ (7)^3-(y)^3-3(7)^2y+3(7)(y)^2\ +\ y^3 \ +\ 27 \ + \ 21 \ (7-y)y \\\\\rightarrow \ 343-y^3-147y+21y^2\ +\ y^3 \ +\ 27 \ + \ 147y-21y^2$

$\rightarrow \ 343+21y^2 \ +\ 27 \ -21y^2 \\\\\rightarrow \ 370 +21y^2 \ -21y^2 \\\\\rightarrow \ 370$

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