SOLUTION: Another problem. Please help. My last question was nicely solved by stanbon(47716) and I salute you. the question is:- When the expression a^+bx+c is divided by x-2, the remainde

Algebra ->  Polynomials-and-rational-expressions -> SOLUTION: Another problem. Please help. My last question was nicely solved by stanbon(47716) and I salute you. the question is:- When the expression a^+bx+c is divided by x-2, the remainde      Log On


   



Question 557526: Another problem. Please help. My last question was nicely solved by stanbon(47716) and I salute you. the question is:-
When the expression a^+bx+c is divided by x-2, the remainder is R. When the expression is divided by x+1, the remainder is still R.
i.) Find the value of b.
ii.) When the expression is divided by x-4, the remainder is 2R. Find the value of c and R.
iii.) When the expression is divided by x-t, the remainder is 5R. Find the two possible values of t.

Answer by KMST(5328) About Me  (Show Source):
You can put this solution on YOUR website!
i.
I suspect you mean
"When the expression C is divided by x-2, the remainder is R. When the expression is divided by x+1, the remainder is still R."
You have a quadratic trinomial P%28x%29=ax%5E2%2Bbx%2Bc
When you divide a polynomial P(x) by (x-a), the original polynomial, P(x), the quotient polynomial, Q(x), and the remainder R, are related through:
P(x)=Q(x)(x-a)+R (and P(a)=R).
So,
P(x)-R = Q(x)(x-a) is divisible by x-a.
In the case of your polynomial, P(x)-R is divisible by x-2 and by x+1.
So it is divisible by
%28x-2%29%28x%2B1%29=x%5E2-x-2
Then P%28x%29-R=ax%5E2%2Bbx%2Bc=a%28x-2%29%28x%2B1%29=a%28x%5E2-x-2%29=ax%5E2-ax-2a and
P%28x%29=a%28x-2%29%28x%2B1%29%2BR=ax%5E2-ax-2a%2BR
So b=-a
ii.
P(4) = a%284-2%29%284%2B1%29%2BR=10a%2BR=2R
10a%2BR=2R --> R=10a
c=-2a%2BR=-2a%2B10a=8a
iii.
P(t) = at%5E2-at%2B8a = 5R = 50a
at%5E2-at%2B8a=50a --> t%5E2-t-42a=0
Factoring, we get t%5E2-t-42a=%28t-7%29%28t%2B6%29
so %28t-7%29%28t%2B6%29=0 has solutions t-7 and t=-6