If B=80°, a=4.1, c=7.1, find the area of the triangle.

14.2 squared units

Step-by-step explanation:

Always draw a diagram for the question. Capital letters are usually angles, and their opposite side is the same letter as a lowercase. (See diagram) The opposite side of angle B is side b.

The formula for area of a triangle is A = bh/2

"A" is for area.

"b" is for base (usually bottom side)

"h" is for height (perpendicular to base).

We know the measurement for the base c = 7.1. We need to find the height.

Notice when you draw in the height, it form two right triangles. We can use trigonometric ratios for right triangles.

Remember the trigonometric ratios using SohCahToa:

sinθ = opposite/hypotenuse;

cosθ = adjacent/hypotenuse and;

tanθ = opposite/adjacent, where θ means the angle of reference.

Focus on the triangle on the left side. We know one angle (∠B = 80°) and one side (a = 4.1). We can find "h", the missing side.

Since ∠B is our angle of reference, "h" is opposite. Since "a" is a longest side, it's the hypotenuse. Use the sine ratio because it uses the opposite and hypotenuse sides.

sinθ = opp/hyp             General sine ratio formula

sinB = h/a                  Variables you use in this problem

sin80° = h/4.1               Isolate "h". Multiply both sides by 4.1

h = 4.1(sin80°)                 Multiply with calculator

h = 4.1(0.98480775...)         Unrounded sin80

h = 4.03771178...                 Round this number

Note the number of decimal places given in the question.

h ≈ 4.0                Round to one decimal place

Now we can use the formula for the area of a triangle.

A = bh/2           Don't confuse side "b" with the base in this question

A = (7.1)(4.0)/2           Simplify the division

A = (7.1)(2.0)                   Multiply

A = 14.2                     Final answer for area

Since we don't know what the units are, you can say the answer is:

A = 14.2u²  or  14.2 squared units

step-by-step explanation:

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