Respuesta :
Answer:
X + 278 = 450; x = 172 cm
Step-by-step explanation:

The given triangle has a perimeter of 450 cm. We know that two of its sides are 128 cm and 150 cm. Using the equation 450 = 278 + x, x = 172 cm.
What is perimeter?
A perimeter is a closed path that encompasses, surrounds, or outlines either a two dimensional shape or a one-dimensional length.
Perimeter of a triangle is the sum of all sides of a triangle.
Side 1 = 128 cm
Side 2 = 150 cm
Side 3 = x cm
Perimeter = 450 cm
Perimeter = side 1 + side 2 + side 3
450 = 128 + 150 + x
x = 450 - 278 cm
x = 172 cm
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