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Look for Relationships If you know a cone'sradius and slant height, what must you dobefore you can find its volume? © MP.7

Sagot :

[tex]\text{Volume}_{cone}=\frac{1}{3}\pi r^2(\sqrt[]{\text{Slant}^2-radius^2})[/tex]

let thev in terms of slant and radius

Explanation

the volume of a cone is given by

[tex]\text{Volume}_{cone}=\frac{1}{3}\pi r^2h[/tex]

where r is the radius and h is the heigth( yellow length)

so, we need to find the heigth in order to use the formula

Step 1

we have then, this triangle

this is a rigth triangle, then let

hypotenuse= slant height

side1 = radius

side2= heigth

we can apply the Pythagorean theorema to find the heigth, the P. T: tell us that the square of the hypotenuse side is equal to the sum of squares of the other two sides,so

[tex]\text{Slant}^2=height^2+radius^2[/tex]

isolate heigth

[tex]\begin{gathered} \text{Slant}^2=height^2+radius^2 \\ \text{subtract }radius^2\text{ in both sides} \\ \text{Slant}^2-radius^2=height^2+radius^2-radius^2 \\ \text{Slant}^2-radius^2=height^2 \\ \text{take the square root in both sides} \\ \sqrt{\text{Slant}^2-radius^2}=\sqrt{height^2} \\ \sqrt[]{\text{Slant}^2-radius^2}=\text{heigth} \end{gathered}[/tex]

therefore, the heigth is

[tex]heigth=\sqrt[]{\text{Slant}^2-radius^2}[/tex]

Step 2

now, replace in the formula

[tex]\begin{gathered} \text{Volume}_{cone}=\frac{1}{3}\pi r^2h \\ \text{Volume}_{cone}=\frac{1}{3}\pi r^2(\sqrt[]{\text{Slant}^2-radius^2}) \end{gathered}[/tex]

Now, we finally get a expression to find the volume when the slant and radius are given.

let the height in terms of slant and radius

I hope this helps you

View image StellalunaZ121319
View image StellalunaZ121319