Where Did I Go Wrong in Simplifying this Algebraic Expression?

[uperkurk]

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

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

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

d^2+4d^2-9d-2

5d^2-9d-2

but wolfram says the answer is

-5d^2-9d+2

What did I do wrong?

 

[HallsofIvy]

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

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

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

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 d^2 into the [9d+(2- 4d^2). Where you were supposed to have -A+ B, you have A- B.

d^2+4d^2-9d-2

5d^2-9d-2

but wolfram says the answer is

-5d^2-9d+2

What did I do wrong?

 

[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.

−d2+[9d+(2−4d2)]

−d2+9d+2−4d2

-5d2 + 9d − 2

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]

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

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

-d^2- 4d^2= -5d^2
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.

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

d^2+4d^2-9d-2

5d^2-9d-2

but wolfram says the answer is

-5d^2-9d+2

What did I do wrong?