3、y=7/(2+5x)
y'=-7*5/(2+5x)²
y''=7*5²*2/(2+5x)³
y'''=-7*5³*2*3/(2+5x)⁴
yⁿ=(-5)ⁿ*(2*3...*n)/(2+5x)ⁿ⁺¹
4、∫₀¹ xe^(1-3x)dx=-1/3*∫₀¹xd[e^(1-3x)]
=-xe^(1-3x)/3|₀¹+1/3*∫₀¹e^(1-3x)dx
=-xe^(1-3x)/3|₀¹-1/9*e^(1-3x)|₀¹
=e/9 -4/(9e²)
6、∫₀⁵ |3x-9|dx=∫₀³ (9-3x)dx+∫₃⁵ (3x-9)
=(9x-3x²/2) |₀³+(3x²/2-9x)|₃⁵
=27/2+75/2-45-(-27/2)
=75/2-18
=37/2