McGraw Hill Glencoe Geometry, 2012
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McGraw Hill Glencoe Geometry, 2012 View details
1. Areas of Parallelograms and Triangles
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Exercise 27 Page 784

The area of a triangle is half the product of its base and its height.

Base: 11m
Height: 8m

Practice makes perfect

We are told that the height of a triangle is 3m less than its base. Therefore, if we let b be the base, the height can be expressed as h=b-3. We are also told that the area is 44 square meters. Let's draw a diagram to illustrate the situation.

The area of a triangle is half the product of its base and its height. A=1/2bhWe can substitute A= 44 and h= b-3 into this formula and solve for b, the base of the triangle. Let's do it!
A=1/2bh
44=1/2b( b-3)
â–Ľ
Solve for b
88=b(b-3)
88=b^2-3b
0=b^2-3b-88
b^2-3b-88=0
Note it's a quadratic equation. To solve this equation we will use the Quadratic Formula. ax^2+ bx+ c=0 ⇕ x=- b± sqrt(b^2-4 a c)/2 a The variable in our equation is b. Let's replace it with x not to mistake it with the b in the Quadratic Formula. b^2-3b-88=0 ⇕ x^2-3x-88=0 Next, we need to identify the values of a, b, and c. x^2-3x-88=0 ⇕ 1x^2+( - 3)x+( - 88)=0 We see that a= 1, b= - 3, and c= - 88. Let's substitute these values into the Quadratic Formula.
x=- b±sqrt(b^2-4ac)/2a
x=- ( - 3)±sqrt(( - 3)^2-4( 1)( - 88))/2( 1)
â–Ľ
Solve for x
x=3±sqrt((- 3)^2-4(1)(- 88))/2(1)
x=3±sqrt(9-4(1)(- 88))/2(1)
x=3±sqrt(9+352)/2
x=3±sqrt(361)/2
x=3 ± 19/2
Now, we can go back to the previous notation and replace x with b. The solutions of our equation are b= 3 ± 192. Let's separate them into the positive and negative cases.
b=3 ± 19/2
b_1=3+19/2 b_2=3-19/2
b_1=22/2 b_2=- 16/2
b_1=11 b_2=- 8

Since b is the base of a triangle it must be positive. Therefore, the base of the triangle is 11m. The height is 3m less than its base, so we can subtract 3 from 11 to obtain the height. Height: 11-3=8 m