a=4,b=3,C=60
c^2=a^2+b^2-2abcosc=4^2+3^2-2*4*3* 1/2 = 13
c=√ 13
sinA = asinC/c = 4 *√3/2/√ 13 = 2√39/ 13
2.
b^2=ac
b^2=a^2+c^2-2accosB
ac=a^2+c^2-2accosB
cosb =(a^2+c^2-ac)/(2ac)=(a^2+c^2)/(2ac)- 1/2
∵(a-c)^2≥0,a^2+c^2≥2ac,(a^2+c^2)/(2ac)≥ 1
∴cosb =(a^2+c^2)/(2ac)- 1/2≥ 1/2
∴0