Angles ratio

The internal angles of a triangle are in ratio 1:4:5. What kind of triangle is it? (solve interior angles and write down and discuss)

Correct answer:

A =  18
B =  72
C =  90

Step-by-step explanation:


A+B+C = 180
B = 4·A
C = 5·A

A+B+C = 180
4A-B = 0
5A-C = 0

Pivot: Row 1 ↔ Row 3
5A-C = 0
4A-B = 0
A+B+C = 180

Row 2 - 4/5 · Row 1 → Row 2
5A-C = 0
-B+0.8C = 0
A+B+C = 180

Row 3 - 1/5 · Row 1 → Row 3
5A-C = 0
-B+0.8C = 0
B+1.2C = 180

Row 3 + Row 2 → Row 3
5A-C = 0
-B+0.8C = 0
2C = 180


C = 180/2 = 90
B = 0-0.8C/-1 = 0-0.8 · 90/-1 = 72
A = 0+C/5 = 0+90/5 = 18

A = 18
B = 72
C = 90

Our linear equations calculator calculates it.

Try calculation via our triangle calculator.




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