Given that equation ax^2 + bx + c = 0 has roots α and β
=> α + β = -b/a
and αβ = c/a
Keeping these in mind, we'll now solve the problems.
1) α^4 + β^4
=> (α²)² + (β²)²
=> (α² + β²)² -
2α²β² by using a² + b² = (a + b)² - 2ab
=> ((α + β)² - 2αβ)²
- 2(αβ)² using the same identity again
We will now substitute the values of α + β and αβ we found in the beginning of the solution
=> ((-b/a)² - 2c/a)² - 2(c/a)²
=> (b²/a² - 2c/a)² - 2c²/a²
=> ((b² - 2ac)/a²)² - 2c²/a²
=> (b² - 2ac)²/a⁴ - 2c²/a²
=> ((b² - 2ac)² - 2a²c²) / a⁴
=> (b⁴ - 4ab²c + 4a²c² - 2a²c²) / a⁴
=> (b⁴ - 4ab²c + 4a²c² - 2a²c²) / a⁴
=> (b⁴ - 4ab²c + 2a²c²) / a⁴
2) α^2/β + β^2/α
=> (α³ + β³)/αβ
=> (α + β)(α² + β² - αβ) /αβ
Again, using a² + b² = (a + b)² - 2ab
=> (α + β)((α + β)² - 3αβ) / αβ
=> (-b/a)((-b/a)² - 3(c/a)) / (c/a)
=> (-b/a)(b²/a² - 3c/a) / (c/a)
=> (-b/c)((b² - 3ac)/ a²)
=> (-b³ + 3abc) / a²c
3) α^3/β + β^3/α
=> (α⁴ + β⁴)/αβ
We've already calculated for (α⁴ + β⁴) in the first question. We will use the result here.
=> ((b⁴ - 4ab²c + 2a²c²) / a⁴) / αβ
=> ((b⁴ - 4ab²c + 2a²c²) / a⁴) / (c/a)
=> (b⁴ - 4ab²c + 2a²c²) / a³c
4) 1/(aα + b) + 1/(aβ + b)
We already know that
α + β = -b/a
=> a(α + β) = -b
=> -a(α + β) = b
Substituting this value of b in the problem,
=> 1/(aα + b) + 1/(aβ + b)
=> 1/(aα - a(α + β)) + 1/(aβ - a(α + β))
=> 1/(-aβ) + 1/(-aα)
=> -1/a (1/β + 1/α)
=> -1/a (α + β)/αβ
=> -1/a (-b/a)(c/a)
=> b/ac
α+β=5 and α²+β²=19 show that αβ=3
ReplyDeleteUse alha plus bheta whole square formula
Deleteα+β=5
Delete=> (α+β)^2 = 25
=> α^2 + β^2 + 2αβ = 25
=> 19 + 2αβ = 25
=> 2αβ = 25 - 19
=> 2αβ = 6
=> αβ = 3
Same qquestio for beta/(a alpa+b) (alpha/a beta+b)
ReplyDeleteThx
ReplyDeleteUse 1/alpha^3+1/beta^3.
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ReplyDelete