Use the method of cylidrincal shells to find the volume of the solid generated by rotating the region bounded by the curves y=6x
1 answer:
Find where the two curves intersect:
<em>y</em> = 6<em>x</em> - 2<em>x</em> ²
<em>y</em> = <em>x</em> ²
6<em>x</em> - 2<em>x</em> ² = <em>x</em> ² → 3<em>x</em> ² - 6<em>x</em> = 3<em>x</em> (<em>x</em> - 2) = 0 → <em>x</em> = 0 and <em>x</em> = 2
Now, for a shell of radius <em>x</em> units away from the axis of revolution, the height of the shell would be the vertical distance between the upper curve and the lower curve. For 0 ≤ <em>x</em> ≤ 2, we have 6<em>x</em> - <em>x</em> ² ≥ <em>x</em> ², so the height of any given shell is (6<em>x</em> - <em>x</em> ²) - <em>x</em> ² = 6<em>x</em> - 2<em>x</em> ².
Then volume of the solid is
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Answer:
x = -3, 0, or 7
Step-by-step explanation:
After removing common factors, the remaining quadratic can be factored by comparison to the factored form of a quadratic.
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<h3>Step 1</h3>Write the equation in standard form.
4x³ -16x² -84x = 0
<h3>Step 2</h3>Factor out the common factor from all terms.
= 4x(x² -4x -21) = 0
<h3>Step 3</h3>Compare to the factored form of a quadratic:
(x +a)(x +b) = x² +(a+b)x +ab
This tells you the constants 'a' and 'b' in the factors can be found by considering ...
(a+b) = -4 . . . . the coefficient of the x term of the quadratic
ab = -21 . . . . . the constant term of the quadratic
It is often helpful to list factor pairs of the constant:
-21 = (-21)(1) = (-7)(3) . . . . integer pairs that have a negative sum
The sums of these pairs are -20 and -4. We are interested in the latter. We can choose ...
a = -7, b = 3
<h3>Step 4</h3>Put it all together.
4x³ -16x² -84 = (4x)(x -7)(x +3) = 0 . . . . . factored form of the equation
<h3>Step 5</h3>Apply the zero product rule. This rule tells you the product of factors will be zero when one or more of the factors is zero:
4x = 0 ⇒ x = 0
x -7 = 0 ⇒ x = 7
x +3 = 0 ⇒ x = -3
Solutions to the equation are x ∈ {-3, 0, 7}.
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<em>Additional comment</em>
What we did in Step 3 is sometimes referred to as the X-method of factoring a quadratic. The constant (ab product) is put at the top of the X, and the sum (a+b) is put at the bottom. The sides of the X are filled in with values that match the product and sum: -7 and 3. The method is modified slightly if the coefficient of x² is not 1.
A graphing calculator often provides a quick and easy method of finding the real zeros of a polynomial.
Answer:
6 swimmers in the first heat can be arranged in 1716 different ways.
Step-by-step explanation:
A swim meet has 13 contestants signed up. To calculate the arrangement of first 6 swimmers in first heat we will use combinations because order doesn't matter.
So to select 6 swimmers out of 13 contestants number of different ways
=
=
=
=
=
= 1716
Therefore, 6 swimmers in the first heat can be arranged in 1716 different ways.