Question 2756: What is r when the problem is 10rSQUARED-96r-40. Can you please show all your steps so I can see how you did it? Answer by gsmani_iyer(201) (Show Source):
You can put this solution on YOUR website!
Before solving this problem, you must bear in your mind that the quadratic problems can be solved even by factorisation and not necessarily by applying the formula i.e. = 0
Choose 2 such numbers, the sum of which should be the coefficient of the mid-term of the expression and at the same time, the product of the same 2 numbers should be the last term multi-plied by coefficient of the 1st term. I hope you understood this. Here in your problem, . The coefficient of the mid-term is -96 and the product of the coefficient of the first term and the last term is -400.
So we have to choose two such numbers as explained above. So find out the factors of -400.
I got -100 and +4. It could be even 100 and -4; but the sum of these(+96) will not be equal to the coefficient of the mid-term. Isn't it? We will proceed further to solve your problem.
= ... (-96r has been splitted as above)
= 10r(r-10) + 4(r-10) ... (factorised the 1st and the last 2 terms)
= (r-10)*(10r+4) ... (Taken out the common factor and the other one)
If (r-10)*(10r+4) = 0
then, (r-10) or (10r+4) has to be = 0
So r = 10; or r = -0.4 Answer.
I hope this is very clear to you now.
