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