SOLUTION: find the whole number such that four times the number subtracted from three times the square of the number makes 15

Question 511720: find the whole number such that four times the number subtracted from three times the square of the number makes 15
Found 2 solutions by nerdybill, oberobic:
Answer by nerdybill(7384) (Show Source): You can put this solution on YOUR website!
find the whole number such that four times the number subtracted from three times the square of the number makes 15
.
Let x = the number
then
3x^2 - 4x = 15
3x^2 - 4x - 15 = 0
replace -4x with:
3x^2 - 9x + 5x - 15 = 0
group terms:
(3x^2 - 9x) + (5x - 15) = 0
factor:
3x(x - 3) + 5(x - 3) = 0
(x - 3)(3x + 5) = 0
x = {3, -5/3}
throw out the fraction since we're looking for whole numbers
x = 3
Answer by oberobic(2304) (Show Source): You can put this solution on YOUR website!
x = a number
.
Three times the square of the number minus four times the number = 15.
3*x^2 - 4x = 15
3x^2 -4x -15 = 0
.
factor
(3x +5)(x -3) = 3x^2 -9x +5x -15 = 3x^2 -4x -15
.
x = -5/3 or 3
.
Obviously, -5/3 is not a whole number, so x =3 is the proposed solution.
.
Check to see if it is correct.
.3x^2 = 3(9) = 27
4x = 12
27-12 = 15
Correct
.
Answer: The whole number is 3.
.
Done.
RELATED QUESTIONS
find the whole number such that four times the number subtracted from the three times... (answered by ankor@dixie-net.com)
find the whole number such that four times the number subtracted from 3 times the square... (answered by mananth)
Find the integer such that four times the number subtracted from twice the square of the... (answered by macston)
Find the whole number such that twice its square subtracted from seven times the number... (answered by dabanfield@earthlink.net)
Find the whole number greater than 0 such that when 5 times the number is subtracted from (answered by Stitch)
Twice a certain whole number subtracted from 3 times the square of the number leaves 133. (answered by Cromlix)
the sum of 1/3 and three times a number is equal to 4/5 subtracted from four times the... (answered by dabanfield)
15 is subtracted from four times a certain number. the result is 7 more than three times... (answered by mananth)
Find two consecutive whole numbers such that 5 times the smaller number added 3... (answered by checkley79)