Basic algebra question

uperkurk

Simplify [itex]-d^2+[9d+(2-4d^2)][/itex]

[itex]-d^2+[9d+(2-4d^2)][/itex]

[itex]d^2[-9d-2+4d^2][/itex]

[itex]d^2+4d^2-9d-2[/itex]

[itex]5d^2-9d-2[/itex]

but wolfram says the answer is

[itex]-5d^2-9d+2[/itex]

What did I do wrong?

HallsofIvy

Here is your error- first, you have dropped the "+" in front of the "[" but that may be just a typo- more importantly you have distributed the "-" in front of [itex]d^2[/itex] into the [itex][9d+(2- 4d^2)[/itex]. Where you were supposed to have -A+ B, you have A- B.

marie.phd

−d2+[9d+(2−4d2)]

−d2+9d+2−4d2

-5d2 + 9d − 2

Mark44

Without any indication that the 2 in d2 is an exponent, what you have here is close to meaningless.
At a minimum, use ^ to indicate exponents, and = for expressions that are equal, like this:

-d^2 + [9d + (2 − 4d^2)]
= -d^2 + 9d + 2 - 4d^2
= -5d^2 + 9d + 2

Even better is to write exponents that actually look like exponents, using the exponent feature that is available when you click Go advanced.

-5d² + 9d + 2

HallsofIvy

[itex]-d^2- 4d^2= -5d^2[/itex]
You seem to be under the impresion that adding two negatives gives a positive. That is not true. That rule only holds for multiplication and division.