Question

A student was asked to use grouping to solve 2x^2−3x−9=0
.

Select the step where the student first made an error.




Given: 2x^2−3x−9=0

Step 1: I need two numbers that multiply to -18 and add to -3. The numbers are -6 and 3.

Step 2: 2x^2−6x+3x−9=0

Step 3: 2x(x−3)−3(x−3)=0

Step 4: (2x−3)(x−3)=0

Step 5: 2x−3=0 and x−3=0

Step 6: x=3/2 and x=3



(1 point)

Step 1

Step 2

Step 3

Step 4

Step 5

Step 6

Answer 1

Step 3.

Error: 3x − 9 factors as +3(x − 3), not −3(x − 3). The correct grouping is 2x(x−3) + 3(x−3) = (2x+3)(x−3).