Question

Find the whole number such that four times the number subtracted from three times the square of the number makes 15.

Answer 1

Let $x$ be the whole number and square of the number will be $x^2$.

It is given that four times the number subtracted from three times the square of the number makes $15$, therefore,

$3x^2-4x=15\Rightarrow 3x^2-4x-15=0\Rightarrow 3x^2-9x+5x-15=0\Rightarrow 3x(x-3)+5(x-3)=0\Rightarrow (3x+5)=0,(x-3)=0\Rightarrow 3x=-5,x=3\Rightarrow x=-\frac{5}{3},x=3$

Since $x$ is a whole number, thus $x=3$.

Hence, the required whole numbers is $3$.