Question

If x = 3, y=-1, find the value of the following expressions :
(i) 4x³– 2y² - 9
(ii) x² - 3y² + 3x​

Answer 1

Given that: x = 3, y = -1

⠀⠀⠀⠀⠀⠀⠀⠀⠀

$\sf \bold{(i) \: 4 {x}^{3} - 2 {y}^{2} - 9}$

⠀⠀⠀⠀⠀⠀⠀⠀⠀

Substitute 3 and -1 in place of x and y respectively.

⠀⠀⠀⠀⠀⠀⠀⠀⠀

⟹⠀$\sf 4 {(3)}^{3} - 2 {( - 1)}^{2} - 9$

⟹⠀$\sf 4(27) - 2(1) - 9$

⟹⠀$\sf 108 - 2 - 9$

⟹⠀$\sf 97$

⠀⠀⠀⠀⠀⠀⠀⠀⠀

The value of the expression will be 97

⠀⠀⠀⠀⠀⠀⠀⠀⠀

$\sf \bold{(ii) \: {x}^{2} - 3 {y}^{2} + 3x}$

⠀

Substitute 3 and -1 in place of x and y respectively.

⠀⠀⠀⠀⠀⠀⠀⠀⠀

⟹⠀$\sf {(3)}^{2} - 3 {( - 1)}^{2} + 3(3)$

⟹⠀$\sf 9 - 3(1) + 9$

⟹⠀$9 - 3 + 9$

⟹⠀$\sf 18 - 3$

⟹⠀$\sf 15$

⠀⠀⠀⠀⠀⠀⠀⠀⠀

Value of the expression will be 15