EmmaH 2 years ago cansomeone show me how to solve this? Use the quadratic formula to find the zeros of the function. y = 16x2 + 40x + 25 {-1.25, 1.25} {-1.25} {-4, 5} {-0.8

1. amistre64

do you recall the setup of the quadratic formula?

2. EmmaH

$\frac{ -b \pm \sqrt{b ^{2}-4ac} }{ 2a }$

3. amistre64

good, and the general form of a quadratic is: $ax^2 + bx + c$ pull the numbers from the problem that relate to the abc parts and what do you get worked out?

4. EmmaH

a=16 b=40 and 25=c

5. amistre64

good, i notice that there are no - signs to worry about so that looks good so far

6. EmmaH

what do i do next?

7. amistre64

plug in those numbers into their abc parts in the formula, the rest is just math for maths sake

8. amistre64

$x=\frac{ -b \pm \sqrt{b ^{2}-4ac} }{ 2a }$ $x=\frac{ -40 \pm \sqrt{40^{2}-4(16)(25)} }{ 2(16) }$

9. EmmaH

$\frac{ -40\pm \sqrt{40^{2}-4(16)(25)} }{ 2(16) }$ is that right?

10. amistre64

looks good to me :)

11. EmmaH

ok then i get 40 pm 16-96/32?

12. EmmaH

but i would end up eith a negative number....

13. amistre64

$\frac{ -40\pm \sqrt{40^{2}-4(16)(25)} }{ 2(16) }$ $\frac{ -40\pm \sqrt{4^2(10)^2-4(4^2)(25)} }{ 2(16) }$ $\frac{ -40\pm 4\sqrt{10^2-4(25)} }{ 2(16) }$ $\frac{ -40\pm 4\sqrt{25(4)-4(25)} }{ 2(16) }$ $\frac{ -40}{ 2(16) }$ $\frac{ -40}{ 2(4.4) }$ $\frac{ -10}{ 2(4) }$ $\frac{ -5}{ 4 }$

14. EmmaH

you lost me at the second one you did how did you get all the the ^2?

15. amistre64

40^2 = (4*10)^2 = 4*10 * 4*10 = 4^2 * 10^2 but you dont have to do exactly what i did

16. EmmaH

uuuuh.....im sorry you lost me all i know is im suppose to square 40 is that what you were doin?

17. EmmaH

@amistre64 ?

18. amistre64

i was doing some manipulations so that i didnt have to worry about computing large numbers and such; i simplified it down to where i recognized the sqrt part goes to zero.

19. amistre64

but 40^2 - 4(16)(25) = 0

20. EmmaH

ui havent learned taht i think im suppose to just use the big numbers

21. amistre64

then math it out for maths sake, youll get big numbers that finally reduce and simplify

22. EmmaH

i tried but i keep getting teh wrong number when i have 40^2-4(16)(5) i get 0 right? i get 1,600 -1,600 and i cant square thaty

23. amistre64

what does 1600 - 1600 equal?

24. EmmaH

0 -_- i cant square 0

25. amistre64

sure you can, 0*0 = 0

26. EmmaH

oooooh......

27. EmmaH

so -40 pm 0/32?

28. amistre64

$\frac{ -40\pm \sqrt{40^{2}-4(16)(25)} }{ 2(16) }$ $\frac{ -40\pm \sqrt{1600-1600} }{ 2(16) }$ $\frac{ -40\pm \sqrt{0} }{ 2(16) }$ $\frac{ -40\pm 0 }{ 2(16) }$ $\frac{ -40}{ 2(16) }$

29. amistre64

yes /32 is fine as well

30. EmmaH

THANK YOU SO MUCH!!!!!

31. amistre64

youre welcome

32. EmmaH

so its -40/32?

33. amistre64

yes, which a calculator should be able to put into decimals for you

34. EmmaH

-1.25?

35. amistre64

correct

36. EmmaH

thank you!