6. If appropriate, assess the integral [xsin(x)dx by substitution. If substitution is not appropriate, mention it, and do not assess. 7. If suitable, assess the integral -dx by substitution. If substitution is not suitable, mention it, and do not assess. Find 4x(x+1)dx by means of two methods: 8. (a) Do the multiplication first, and then anti-differentiate. (b) Use the substitution w = x. 9. (c) Explain how the expressions from parts (a) and (b) are different. Are they both correct? Evaluate (-sinx)dx by using the method of substitution. 10. Evaluate [secx dx by using the method of substitution.