find the x-intercepts of the parabola -4.9t^2 + 5t +12.5
Usually we just do this:
___ X ___ = 12.5X-4.9
---+---= 5
but it doesnt work with decimals...

Question

find the x-intercepts of the parabola -4.9t^2 + 5t +12.5
Usually we just do this:
___ X ___ = 12.5X-4.9
---+---=  5
but it doesnt work with decimals...

anonymous · Answer

Do you know the quadratic formula?

anonymous · Answer

no
but our teacher told us not to use it

anonymous · Answer

dont you have to find factors of 12.5 X -4, that add to 5? but this doesnt work with decimals

anonymous · Answer

12.5 X -4.9  *

anonymous · Answer

Well, if you have learned it, you could try completing the square... but if you're not allowed the quadratic formula you might not have learned this. http://www.purplemath.com/modules/sqrquad.htm Are you saying that you usually factor this? This is factorable (with irrational roots), from what I can tell at first glance.

anonymous · Answer

Oh, yeah, so:

$$ -10 (-4.9t^2 +5t +12.5) = -10(0) \
49t^2 -50t -125 = 0 $$

anonymous · Answer

I multiplied both sides by $-10$ so it's easier to work with.

raden · Answer

it can't be factorized

anonymous · Answer

he just did it ^

anonymous · Answer

didnt he?

raden · Answer

just use quadratic formula

anonymous · Answer

which is?

raden · Answer

49t^2−50t−125=0
just check the value of discriminant (D)
D=b^2-4ac = (-50)^2 - 4(49)(-125) = 2500 + 24.500 = 27,000
sqrt(27,000) isnt a integer numbr

anonymous · Answer

i dont understand

anonymous · Answer

cant you factorise it like muntoo

anonymous · Answer

oi muntoo,
wouldnt the second line where you times both sides by ten be this?
49t^2 - 50t - 125 = -10

anonymous · Answer

how do you get the right side to equall 0?

raden · Answer

dont forget, not all quadratic equation can be factorized
so, to find its solution just use quadratic formula :
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