Question

Please help!

1.For which value of x does the graph of y = 3x2 − 2x − 5 cross the x-axis?

2.What are the approximate solutions of 2x2 + 9x = 8 to the nearest hundredth?

Answer 1

an easy method for both problems is to use the general quadratic formula

Answer 2

i dont know how... i was sick for the week they tought this

Answer 3

ok... for a quadratic \[ax^2 + bx + c = 0\] the roots of zeros can be found using \[x = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a}\]

Answer 4

in your 1st question a = 3, b = -2 and c = -5

substitute them and then calculate the 2 answers

Answer 5

so... x=-1/3?

Answer 6

@campbell_st

Answer 7

not quite when you substitute its \[x = \frac{2 \pm \sqrt{(-2)^2 - 4 \times 3 \times (-5)}}{2 \times 3} = \frac{2 \pm 8}{6}\]

so you have 2 solutions \[x = \frac {2 + 8}{6}~~~~~and~~~~~x = \frac{2 - 8}{6}\]

just simplify them

Answer 8

so.. -1?

Answer 9

-1 one is correct right @campbell_st

Answer 10

that's correct... and the other is..?

Answer 11

i cant figure it out...

Answer 12

2^{2} +9x =8

Answer 13

can you please show me how to do it @campbell_st ?

Answer 14

add you needed to do for the 2nd intercept is simplify \[x = \frac{-2 -8}{6} = \frac{-10}{6} ~~~so~~~~x = \frac{-5}{3} \]

Answer 15

(2) rewrite the equation \[2x^2+ 9x - 8 = 0\]

so using the formula you get

\[x = \frac{-9 \pm \sqrt{9^2 - 4 \times 2 \times -8}}{2 \times 2}\]

so there are 2 solutions \[x = \frac{-9 + \sqrt{9^2 - 4 \times 2 \times -8}}{2 \times2}~~and~~~x = \frac{-9 - \sqrt{9^2 - 4 \times 2 \times -8}}{2 \times 2}\]

just calculate the answers

Answer 16

the queston says the solution to the nearest hundredth... so use a calculator and the round the answers to 2 decimal places.

Answer 17

so you need to solve to 2 decimal places

\[x = \frac{-9 + \sqrt{145}}{4}~~~and~~~ x = \frac{-9 - \sqrt{145}}{4}\]