三角形ABC中,角A,B,C对应的边分别是abc,若sinA,sinB,sinC成等差数列,且...答:sinA,sinB,sinC成等差数列,且tanC=2根号2,则有sinC=2/3根号2,cosC=1/3 即有2sinB=sinA+sinC,即有2b=a+c cosC=(a^2+b^2-c^2)/(2ab)=(a^2+b^2-(2b-a)^2)/(2ab)=(a^2+b^2-4b^2+4ab-a^2)/(2ab)=(4ab-3b^2)/(2ab)=2-3b/(2a)=1/3 即有3b/(2a)=5/3 ...
在三角形ABC中,若sinB/cosC>根号2,求c的取值范围答:首先,sinB/cosC>0,由于sinB>0,所以cosC>0,C<90°;sinB/cosC>√2,sinB>√2cosC,由于sinB≤1,所以cosC<√2/2,即C>45°,而C<90°,故C的取值范围为(45°,90°).
sina的平方减cosb的平方加根号2倍的sinasinb等于负cosc的平方...答:由sinA平方=sinB平方+sinC平方,利用正弦定理得a^2 = b^2+ c^2,(a^2表示a的平方)故△ABC是直角三角形,且∠A=90°,∴B+C=90°,B=90°-C,∴sinB=cosC,∴由sinA=2sinB cosC可得:1=2sin2B,∴sinB2 =1/2 ,sinB=根号2/2 ,∴B=45°.∴△ABC是等腰直角三角形.
...3,tan((A+B)/2)+tan(c/2)=4,2sinBcosC=sinA,求A,B及b,c答:Home Accessibility Sitemap About Contact Blogs Videos Tools Log in or create an account Go to HealthSpace ,bvlgari men watches Learn about patient choice now Whether you're planning to have a baby,omega seamaster, are already pregnant,bulgari watch, or your new baby has just arrived...