Step by Step Solution
Step by step solution :
Step 1 :
Trying to factor as a Difference of Cubes:
1.1 Factoring: x3-30
Theory : A difference of two perfect cubes, a3 - b3 can be factored into
(a-b) • (a2 +ab +b2)
Proof : (a-b)•(a2+ab+b2) =
a3+a2b+ab2-ba2-b2a-b3 =
a3+(a2b-ba2)+(ab2-b2a)-b3 =
a3+0+0-b3 =
a3-b3
Check : 30 is not a cube !!
Ruling : Binomial can not be factored as the difference of two perfect cubes
Polynomial Roots Calculator :
1.2 Find roots (zeroes) of : F(x) = x3-30
Polynomial Roots Calculator is a set of methods aimed at finding values of x for which F(x)=0
Rational Roots Test is one of the above mentioned tools. It would only find Rational Roots that is numbers x which can be expressed as the quotient of two integers
The Rational Root Theorem states that if a polynomial zeroes for a rational number P/Q then P is a factor of the Trailing Constant and Q is a factor of the Leading Coefficient
In this case, the Leading Coefficient is 1 and the Trailing Constant is -30.
The factor(s) are:
of the Leading Coefficient : 1
of the Trailing Constant : 1 ,2 ,3 ,5 ,6 ,10 ,15 ,30
Let us test ....
P | Q | P/Q | F(P/Q) | Divisor | |||||
---|---|---|---|---|---|---|---|---|---|
-1 | 1 | -1.00 | -31.00 | ||||||
-2 | 1 | -2.00 | -38.00 | ||||||
-3 | 1 | -3.00 | -57.00 | ||||||
-5 | 1 | -5.00 | -155.00 | ||||||
-6 | 1 | -6.00 | -246.00 | ||||||
-10 | 1 | -10.00 | -1030.00 | ||||||
-15 | 1 | -15.00 | -3405.00 | ||||||
-30 | 1 | -30.00 | -27030.00 | ||||||
1 | 1 | 1.00 | -29.00 | ||||||
2 | 1 | 2.00 | -22.00 | ||||||
3 | 1 | 3.00 | -3.00 | ||||||
5 | 1 | 5.00 | 95.00 | ||||||
6 | 1 | 6.00 | 186.00 | ||||||
10 | 1 | 10.00 | 970.00 | ||||||
15 | 1 | 15.00 | 3345.00 | ||||||
30 | 1 | 30.00 | 26970.00 |
Polynomial Roots Calculator found no rational roots
Equation at the end of step 1 :
x3 - 30 = 0
Step 2 :
Solving a Single Variable Equation :
2.1 Solve : x3-30 = 0
Add 30 to both sides of the equation :
x3 = 30
When two things are equal, their cube roots are equal. Taking the cube root of the two sides of the equation we get:
x = ∛ 30
The equation has one real solution
This solution is x = ∛30 = 3.1072
One solution was found :
x = ∛30 = 3.1072How did we do?
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