Relevance
• Anonymous
9 years ago

We have 7d^2 - 21d to solve. Here's the solution:

Given: 7d^2 - 21d

We take out d has the common factor. This gives us:

7d (d - 3) (this is a half equation)

We need to make 7d (d - 3) into a FULL equation. To do this, we'll equate 7d (d-3) to 0. This gives us:

7d (d - 3) = 0

Now we have to ask ourself "what value of d will make the left hand side of the equation equal to 0.

One value is d = 0. If d = 0 then left side will become 0 and we'll have 0 = 0. So thats one answer

another value is d = 3. if d = 3, then the bracket (3-3) will give us 0 and 0 multiplied by anything is 0.

So the answer is : d = 0 and d = 3

For these kind of equations, the idea is to find for which value the equation will balance. (left side = right side).

• 9 years ago

factor it, i.e. take "7d" out of both of them because it is the highest amount that you can divide by in both of them

7d(d-3)

can you take it from there buddy? solve 7d for zero, and solve d-3 for zero