Pearson Geometry Common Core, 2011
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Pearson Geometry Common Core, 2011 View details
2. Special Right Triangles
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Exercise 33 Page 505

Practice makes perfect
a The diagonal of a cube forms a hypotenuse of a triangle with legs along the diagonal of the base and the edge of the cube. We know that the leg along the edge of the base is equal to 1 unit. Let's look at the base of the cube.
Let's use the Pythagorean Theorem to find the length of the base's diagonal.
a^2+b^2=c^2
1^2+ 1^2=c^2
1+1=c^2
2=c^2
sqrt(2)=c
We have found that the legs of the triangle are equal to 1 unit and sqrt(2) units.

Let's draw the triangle formed.

Let's plug in the values for the legs of this triangle into the Pythagorean Theorem to find the length of d, the diagonal of the cube.
a^2+b^2=c^2
1^2+( sqrt(2))^2=c^2
1+2=c^2
3=c^2
sqrt(3)=c
The length of the diagonal with edges of length 1 unit is equal to sqrt(3) units.
b Let's repeat the process from Part A with edges of length 2 units this time. We will start by finding the diagonal of the base, which is the length of the other leg.
a^2+b^2=c^2
2^2+ 2^2=c^2
4+4=c^2
8=c^2
sqrt(8)=c
We have found that the legs of the triangle are equal to 2 units and sqrt(8) units. Finally, let's plug in these values into the Pythagorean Theorem to find the length of d, the diagonal of the cube.
a^2+b^2=c^2
2^2+( sqrt(8))^2=c^2
4+8=c^2
12=c^2
sqrt(12)=c

Write as a product

sqrt(4 * 3)=c
sqrt(4) * sqrt(3)=c
2sqrt(3)=c
The length of the diagonal with edges of length 2 units is equal to 2sqrt(3) units.
c Let's repeat the same process from Parts A and B with edges of length s units this time. We will start by finding the length of the other leg.
a^2+b^2=c^2
s^2+ s^2=c^2
2s^2=c^2
sqrt(2s^2)=c
We have found that the legs of the triangle are equal to s units and sqrt(2s^2) units. Finally, let's plug in these values into the Pythagorean Theorem to find the length of d, the diagonal of the cube.
a^2+b^2=c^2
s^2+( sqrt(2s^2))^2=c^2
s^2+2s^2=c^2
3s^2=c^2
sqrt(3s^2)=c
sqrt(3) * sqrt(s^2)=c
sqrt(3)s=c
The length of the diagonal with edges of length s units is equal to ssqrt(3) units. We can see this relationship applies in Parts A and B, where the edges were s= 1 and s= 2. In these cases, we found diagonals of lengths sqrt(3) and 2sqrt(3) units, respectively.