Write down the integral to evaluate
∫x7dx Identify exactly what must be integrated.
Identify the type of function
integrand=x7 Recognise it as a power of x so we know which rule to use.
Recall the relevant standard result
∫xndx=n+1xn+1+c (n=−1) This is the formula-book result for this type of function.
Apply the standard result
∫x7dx=8x8 Substitute into the standard result.
Check by differentiating the result
dxd(8x8)=x7 Differentiating the proposed answer returns the integrand.
Include the constant of integration
8x8+c Indefinite integrals require the arbitrary constant c.
Eliminate the first incorrect option
x8+c does not differentiate to x7 Its derivative is not the integrand, so it is rejected.
Eliminate the second incorrect option
7x8+c does not differentiate to x7 Its derivative is not the integrand, so it is rejected.
Eliminate the third incorrect option
7x6+c does not differentiate to x7 Its derivative is not the integrand, so it is rejected.
Eliminate the fourth incorrect option
8x7+c does not differentiate to x7 Its derivative is not the integrand, so it is rejected.
Note the common coefficient error
divide by the coefficient; do not multiply A frequent mistake is multiplying by the constant instead of dividing.
Note the common sign error
keep the sign given by the standard result Sine and cosine integrals change sign, so check carefully.
Restate the standard result in general form
∫xndx=n+1xn+1+c (n=−1) The same rule applies to every function of this type.
Confirm the coefficient in the answer
The coefficient comes directly from the standard result.
Select the correct option
8x8+c This is the only expression whose derivative is the integrand.