2
VIII Глава.
Производная и ее геометрический смысл
§ 44 Производная
№ 776.
s(t)=1+3t; v
cp
=
h
)t(s)ht(s −+
. T.k. s(t)=1+3t, то s(t+h)–st=
=1+3(t+h)– (1+3t)=1+3t+3h–1–3t=3h, поэтому v
cp
=
h
h3
=3. Проверим
результат в случаях, приведенных в условии:
1) h=4–1=3, s(t+h)=1+3⋅4=13, s(t)=1+3⋅1=4, v
cp
=
3
413 −
=3;
2) h=1–0,8=0,2, s(t+h)=1+3⋅1=4, s(t)=1+3⋅0,8=3,4, v
cp
=
2,0
6,0
2,0
4,34
=
−
=3.
№ 777.
1) s(t)=2t; v
cp
=
h
h2
h
t2)ht(2
h
)t(s)ht(s
=
−+
=
−+
=2
Проверим: h=1,2–1=0,2
s(t+h)=2⋅1,2=2,4; s(t)=2⋅1=2; v
cp
=
2,0
4,0
2,0
24,2
=
−
=2
2) s(t)=t
2
t=1; (t+h)=1,2;
v
cp
= =
−++
=
−+
=
−+
h
thth2t
h
t)ht(
h
)t(s)ht(s
22222
=2t+h=2⋅1+(1,2–1)=2,2.
№ 778.
1) s(t)=2t+1;
а) s(t+h)–s(t)=2(t+h)+1–2t–1=2t+2h+1–2t–1=2h;
б) v
cp
=
h
h2
h
)t(s)ht(s
=
−+
=2; в) 2limvlim
0h
cp
0h →→
=2;
2) s(t)=2–3t;
а) s(t+h)–s(t)=2–3(t+h)–2+3t=2–3t–3h–2+3t= –3h;
б) v
cp
=
h
h3
h
)t(s)ht(s
−=
−+
= –3; в) )3(limvlim
0h
cp
0h
→→
= –3.
№ 779.
s(t)=0,25t+2
1) h=8–4=4;
v
cp
=
)
4
2122
4
2425,024425,0)()( −−+
=
−⋅−++⋅
=
−+
h
tshts
=0,25
2) v(t)=
25,0limvlim
0h
cp
0h →→
=
=0,25.