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# straight line

Two lines pass through (4,3) and each line makes an angle 45°with the line y=1/3x. find the equations of the two lines.

### 1 Answer

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- 1 decade agoFavorite Answer
設L:y=mx+c

tan45°=∣(m-1/3) / [1+m/3] ∣

±1= (3m-1) / (3+m) [[[(右邊分子分母乘3)]]]

3+m=3m-1 or -3-m=3m-1

2m=4 or 4m=-2

m=2 or -1/2

∴y=2x+c and

y=-1/2+c

put(4,3)

3=2(4)+c , 3=-1/2(4)+c

c=-5 , c=5

two lines

y=2x-5

y=-1/2+5

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