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5x+cosx=0show that the equation 5x+cosx=0 has a solution.Are there many solution?

题目详情
5x+cosx=0
show that the equation 5x+cosx=0 has a solution.Are there many solution?
▼优质解答
答案和解析
令f(x)=5x+cosx
f'(x)=5-sinx,由于·-1≤sinx≤1
所以5-sinx>0
于是f(x)为单调增函数
于是f(x)=0仅有一解
即5x+cosx=0仅有一根