# Giải bài 1 trang 66 - Sách giáo khoa Toán 8 tập 1

##### Hướng dẫn giải

Hình 5 :

a) Ta có : $$\hat{A} + \hat{B} + \hat{C} + \hat{D} = 360^0$$ $$\Rightarrow 110^{\circ}+120^{\circ}+80^{\circ}=360^{\circ} + x = 360^0$$

$$\Rightarrow 310^0 +x = 360^0$$  $$\Rightarrow$$$$x = 360^0 - 310^0 = 50^0$$.

b) Ta có : $$\hat{E} + \hat{F} + \hat{G} + \hat{H} = 360^0$$ $$\Rightarrow 90^{\circ}+90^{\circ} +x +90^{\circ}=360^{\circ}$$

$$\Rightarrow 270^0 +x = 360^0 \Rightarrow x = 360^0-270^0=90^0$$

c) Ta có : $$\hat{A} + \hat{B} + \hat{C} + \hat{D} = 360^0$$$$\Rightarrow 65^0 +90^0 +x +90 ^0 = 360^0$$

$$\Rightarrow 245^0 + x = 360^0 \Rightarrow x = 360^0 -245^0 = 115^0$$

d) Ta có : $$\hat{M} + \hat{N} + \hat{I} + \hat{K} = 360^0$$

$$\Rightarrow ( 180^0 - 105^0) +x + 90^0 + (180^0-60^0) = 360^0$$

$$\Rightarrow 75^0 + x + 90^0 + 120^0 = 360^0 \Rightarrow 285^0 + x = 360^0$$

$$\Rightarrow x = 360^0 - 285^0 = 75 ^0$$

Hình 6 :

a)  Ta có : $$\hat{P} + \hat{Q} + \hat{R} + \hat{S} = 360^0 \Rightarrow x + x + 95^0 +65^0 = 360^0$$

$$\Rightarrow 2x + 160^0 = 360^0 \Rightarrow 2x = 360^0 - 160^0 = 200^0 \Rightarrow x=100^0.$$

b) Ta có : $$\hat{M} + \hat{N} + \hat{P} + \hat{Q} = 360^0$$$$\Rightarrow 3x + 4x + x + 2x = 360^0$$

$$\Rightarrow 10x = 360^0 \Rightarrow x = 36^0.$$

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