Răspuns:
Explicație pas cu pas:
c)
[tex]\\\\ h_{a} =\frac{2S}{a} =\frac{2\frac{absinC}{2} }{a} =\frac{absinC}a} =bsinC\\\\ h_{a} =\frac{2S}{a} =\frac{2\frac{acsinB}{2} }{a} =\frac{acsinB}a} =csinB[/tex]
d)
bcosB + ccosC = (asinB/sinA)cosB + (asinC/sinA)cosC =
= (a/sinA)(sinBcosB + sinCcosC) =
= (a/sinA)(sinBcosB + sinCcosC) =
= (a/sinA)(sin2B/2 + sin2C/2) =
= (a/sinA)(sin2B + sin2C)/2 =
= (a/sinA)[2sin(B + C)cos(B - C)]/2 =
= (a/sinA)sin(pi - A)cos(B - C) =
= (a/sinA)sinAcos(B - C) =
= acos(B - C)
