Some times you do. If you know all of the side lengths, then you can just add them to find the perimeter, if one of the sides is the same as the height, then you may need to find it.
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To find the area of a triangle, you need the length of the base and the height. If the triangle has a base of 19 cm and a height of 21 cm, the area would be (1/2) * base * height = (1/2) * 19 cm * 21 cm = 199.5 cm^2. To find the perimeter of a triangle, you need to add the lengths of all three sides. Without knowing the lengths of the other sides, the perimeter cannot be determined.
There is no rule for the perimeter of an acute triangle. You simply need to add the sides.
The answer depends on what information you have but, basically, you need to add together the lengths of the three sides of the triangle.
The perimeter is the sum of all four sides, so you need to calculate 2 x length + 2 x height. The fact that the rectangle is at the bottom of a triangle is irrelevant - except that in specific diagrams, information may be provided that lets you calculate the length or the width of the triangle.
1/2bh b=base h=height To find the are of a triangle,you have to multiply the base times height and divide the answer by 2. To find the area of a triangle you need to multiply all the sides of the triangle and then divide by 2.