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- KrishnamurthyLv 71 month ago
(2a + 3)(5a - 7)
= 10a^2 + a - 21
- 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
in each case describing the product of one possible pair of terms, one from each of the expressions being multiplied.