How do you evaluate #sum_(k=5)^26 4#?

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Answer 1 · 2016-07-03T16:39:55

#88#

The usual sum representation is

#S=sum_{i=i_{min}}^{i=i_{max}}s_i#

in this case #s_i = 4#, #i_{min}=5#,#i_{max}=26#

The short notation is for

#S = s_{i_min}+s_{i_min+1}+s_{i_min+2}+cdots+s_{i_{max}}#

in the present case we have

#S= s_5+s_6+s_7+cdots+s_26#

#S= 4_5+4_6+4_7+cdots+4_26#

#S= 4(1_5+1_6+1_7+cdots+1_26)#

#S = 4(i_{max}-i_{min}+1) = 4(26-5+1) = 88#