Solve ∫ (from 1 to 4) of (3x^2-9x) wrt x

$$\int _ { 1 } ^ { 4 } ( 3 x ^ { 2 } - 9 x ) d x$$

Evaluate

$$-\frac{9}{2}=-4.5$$

Solution Steps

Evaluate the indefinite integral first.

$$\int 3x^{2}-9x\mathrm{d}x$$

Integrate the sum term by term.

$$\int 3x^{2}\mathrm{d}x+\int -9x\mathrm{d}x$$

Factor out the constant in each of the terms.

$$3\int x^{2}\mathrm{d}x-9\int x\mathrm{d}x$$

Since \int x^{k}\mathrm{d}x=\frac{x^{k+1}}{k+1} for k\neq -1, replace \int x^{2}\mathrm{d}x with \frac{x^{3}}{3}. Multiply 3 times \frac{x^{3}}{3}.

$$x^{3}-9\int x\mathrm{d}x$$

Since \int x^{k}\mathrm{d}x=\frac{x^{k+1}}{k+1} for k\neq -1, replace \int x\mathrm{d}x with \frac{x^{2}}{2}. Multiply -9 times \frac{x^{2}}{2}.

$$x^{3}-\frac{9x^{2}}{2}$$

The definite integral is the antiderivative of the expression evaluated at the upper limit of integration minus the antiderivative evaluated at the lower limit of integration.

$$4^{3}-\frac{9}{2}\times 4^{2}-\left(1^{3}-\frac{9}{2}\times 1^{2}\right)$$

Simplify.

$$-\frac{9}{2}$$