Ответ: ∡B= 135°
Объяснение:
BA=(Xa-Xb;Ya-Yb;Za-Zb)=(2-(-1); 1-1;7-3) =(3;0;4)
BC=(Xc-Xb;Yc-Yb;Zc-Zb)=(-8-(-1); 1-1;2-3) =(-7;0;-1)
IBAI²=3²+0²+4² =25
IBAI=5
IBCI²=(-7)²+0²+(-1)² =50
IBCI=5√2
BA*BC =Xba*Xbc+Yba*Ybc+Zba*Zbc=3*(-7)+0+4*(-1)=-25
IBAI*IBCI*cos∡B= BA*BC
=> 5*5√2*cos∡B= -25
25*√2*cos∡B= -25
cos∡B= -25/(25*√2)
cos∡B= -1/√2 = -√2/2
=>∡B= 135°
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Ответ: ∡B= 135°
Объяснение:
BA=(Xa-Xb;Ya-Yb;Za-Zb)=(2-(-1); 1-1;7-3) =(3;0;4)
BC=(Xc-Xb;Yc-Yb;Zc-Zb)=(-8-(-1); 1-1;2-3) =(-7;0;-1)
IBAI²=3²+0²+4² =25
IBAI=5
IBCI²=(-7)²+0²+(-1)² =50
IBCI=5√2
BA*BC =Xba*Xbc+Yba*Ybc+Zba*Zbc=3*(-7)+0+4*(-1)=-25
IBAI*IBCI*cos∡B= BA*BC
=> 5*5√2*cos∡B= -25
25*√2*cos∡B= -25
cos∡B= -25/(25*√2)
cos∡B= -1/√2 = -√2/2
=>∡B= 135°