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### 2 Answers

- SamwiseLv 71 month ago
I'm guessing a possible typo here, because the = sign makes little sense. Perhaps it was supposed to be a - sign (one key to the left) or a + sign (same key, but shifted).

In case it's either of those, here are the evaluations:

(2a-3)(5a-7) = 10a^2 - 15a - 14a + 21 = 10a^2 - 29a + 21

[where "a^2" is the usual way around here of writing "a to the power of 2"].

(2a+3)(5a-7) = 10a^2 + 15a - 14a - 21 = 10a^2 + a - 21

The expansion method I used is known by the mnemonic F.O.I.L., which stands for

First

Outer

Inner

Last

in each case describing the product of one possible pair of terms, one from each of the expressions being multiplied.