Why is a negative exponent minus a positive exponent a negative exponent?
when you're doing a problem like that use this trick. let's say
you have 3 to the -7 power minus 3 to the 4 power. -7 - 4 can also
be shown as -7 + -4. i switched the minus sign to a plus sign and
because i did that, i had to switch the positive 4 to a negative 4.
so i got 3 to the -7 power plus 3 to the -4 power.