Problem 1:

exponent for e = u = 5x, du = 5 dx, "fix" the 5 | |

Problem 2:

u = x², du = 2x dx, "fix" the 2 | |

Problem 3:

This is a fraction, but the numerator is not the derivative of the denominator. It is not a log. It is also not a single power of e. | |

Rewrite the integrand as two fractions and simplify using exponent rules. | |

Problem 4:

Rewrite the integrand first. | |