SOLUTION: I need some help with 3 math problems I am getting started but cant get finished can some please so me what I am doing wrong These 2 problems are directions use the square root pro

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Question 148929: I need some help with 3 math problems I am getting started but cant get finished can some please so me what I am doing wrong These 2 problems are directions use the square root property to solve the following
7x^2=21 i got +/- square root of 3

(z+3)^2=8 i started like this

z+3=8 z+5 so my ans is z=5 of z=-5

This problems direction is complete using the quadratic formula to solve
15T^2 + 7T - 2 = 0
x=7 square root 14-4 x 15 x 7 = 14-420/30 = -406/30 and thats where I get stuck Thanks for the help Leann
Answer by checkley77(12844) (Show Source):
You can put this solution on YOUR website!
7x^2=21
x^2=21/7
x^2=3
x=sqrtr3
x=+/-1.732 answer.
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(z+3)^2=8
first you must square the (z+3) term.
z^2+6z+9=8
z^2+6z+9-8=0
z^2+6z+1=0
using the quadratic equation:
z=(-6+-sqrt[6^2-4*1*1])/2*1
z=(-6+-sqrt[36-4])/2
z=(-6+-sqrt32)/2
z=(-6+-5.65685)/2
z=-.343/2
z=-.17165 answer.
z=(-6-5.65685)/2
z=-11.65685/2
z=-5.828 answer.
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15T^2+7T-2=0
already used the quadratic formula.
this problem can be factored without the formula thus:
(5t-1)(3t+2)=0
5t-1=0
5t=1
t=1/5
t=.2 answer.
3t+2=0
3t=-2
t=-2/3
t=-.66667 answer.
if you insist on the quadratic formula then:

t=(-7+-sqrt7^4-4*15*-2])/2*15
t=(-7+-sqrt[49+120])/30
t=(-7+-sqrt169)/30
t=(-7+-13)/30
t=(-7+13)/30
t=6/30
t=.2 answer.
t=(-7-13)/30
t=-20/30
t=-2/3=-.66667 answer.
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comment: don't know where you got your math instructions but they are not correct.