等差数列中,a3=7,a10-a5=15则an=?帮我,教我,

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等差数列中,a3=7,a10-a5=15则an=?帮我,教我,等差数列中,a3=7,a10-a5=15则an=?帮我,教我,等差数列中,a3=7,a10-a5=15则an=?帮我,教我,a3=7,a1

等差数列中,a3=7,a10-a5=15则an=?帮我,教我,
等差数列中,a3=7,a10-a5=15则an=?
帮我,教我,

等差数列中,a3=7,a10-a5=15则an=?帮我,教我,
a3=7,
a10-a5=5d=15
所以
d=3
an=a3+(n-3)*d
=7+(n-3)*3
an=3n-2.

a10-a5=15
a5+5d-a5=15
5d=15
d=3
a3=a1+2d
7=a1+2*3
a1=1
an=a1+(n-1)d
=1+3(n-1)
=3n-2