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# please i really need help

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2z^2-11z-21

Guest Apr 5, 2017

#2
+7324
+2

To factor this:

2z2 - 11z - 21

Split the middle term.

What two numbers add to -11 and multiply to (-21)(2)= -42 ? → -14 and 3

2z2 - 14z + 3z - 21

(2z2 - 14z) + (3z - 21)

Factor a 2z out of the first term and factor a 3 out of the second term.

2z(z - 7) + 3(z - 7)

Factor a (z - 7) out of both terms.

(2z + 3)(z - 7)

hectictar  Apr 5, 2017
#1
+7481
+1

2z^2-11z-21

$$2z^2-11z-21$$

$$z = {11 \pm \sqrt{121+168} \over 4}=\frac{11\pm 17}{4}$$

$$z_1=7\\z_2=-1.5$$

$$2z^2-11z-21=2 \times(z-7)\times (z+1.5)$$

!

asinus  Apr 5, 2017
edited by asinus  Apr 5, 2017
#2
+7324
+2

To factor this:

2z2 - 11z - 21

Split the middle term.

What two numbers add to -11 and multiply to (-21)(2)= -42 ? → -14 and 3

2z2 - 14z + 3z - 21

(2z2 - 14z) + (3z - 21)

Factor a 2z out of the first term and factor a 3 out of the second term.

2z(z - 7) + 3(z - 7)

Factor a (z - 7) out of both terms.

(2z + 3)(z - 7)

hectictar  Apr 5, 2017