If the zeroes of the polynomial f(x)=x²-p(x 1)-c are alpha &beta then ...
Given that alpha and beta are the roots of the quadratic equation f(x) = x^2-p(x+1)-c = x^2-px-p-c =
x^2 -px-(p+c),comparing with
ax^2 + bx + c, we have, a =1 , b= -p & c= -(p+c)
alpha+beta = -b/a = -(-p)/1 = p
& alpha*beta = c/a = -(p+c)/1 = -(p+c)
Therefore,
(Alpha + 1)*(beta+1)
= Alpha*beta + alpha + beta + 1
= -(p+c) + p + 1
= -p-c+p+1
= 1-c
If the zeroes of the polynomial f(x)=x²-p(x 1)-c are alpha &beta then ...
And beta, then we can write:
f(x) = (x-alpha)(x-beta)
Expanding this out, we get:
f(x) = x² - (alpha+beta)x + alpha*beta
Comparing this to the given expression for f(x), we see that:
p(1) = alpha+beta
c = alpha*beta
To find the value of p(2), we note that:
p(x) = f(x) + x
So:
p(2) = f(2) + 2
We can find f(2) by plugging in x=2 into the expression for f(x):
f(2) = 2² - p(1)*2 - c
Using the values we found earlier for p(1) and c, we have:
f(2) = 4 - (alpha+beta)*2 - alpha*beta
Now we need to express alpha+beta and alpha*beta in terms of p(2). To do this, we use the following identities:
(alpha+beta)² = alpha² + 2alpha*beta + beta² = (alpha+beta)² - 2alpha*beta
(alpha*beta)² = alpha²*beta² = (alpha*beta)²
Adding these two equations, we get:
(alpha+beta)² + (alpha*beta)² = (alpha+beta)² - 2alpha*beta + (alpha*beta)²
Simplifying, we have:
2(alpha*beta)² + 2alpha*beta = (alpha+beta)²
Using the values we found earlier for alpha+beta and alpha*beta, we have:
2c² + 2p(1)c = p(1)²
Substituting in the expression we found earlier for p(1), we have:
2c² + 2(p(2)-c)p(1) = p(1)²
Simplifying, we get:
2c² + 2p(2)p(1) - 2c*p(1) = p(1)²
Substituting in the expression we found earlier for c, we have:
2(alpha*beta)² + 2p(2)(alpha+beta) - 2(alpha*beta)(alpha+beta) = (alpha+beta)²
Simplifying, we get:
2(alpha+beta)(alpha*beta-p(2)) = 0
Since alpha and beta are distinct zeroes of f(x), we know that alpha+beta ≠ 0. Therefore, we must have:
alpha*beta - p(2) = 0
Solving for p(2), we get:
p(2) = alpha*beta = c
Therefore, we have:
p(2) = c = alpha*beta
as desired.