Seminar 6: de nirea functiilor trigonometrice sin si cos ...
[Pages:2]Seminar 6: denirea functiilor trigonometrice sin si cos, proprietatile lor, formule trigonometrice
1. Folosind denitia functiilor trigonometrice sin si cos, determinati valoarea acestor functii pentru
3 2 5 4 3 7 5 4 8 19
, , , , , , , , , , , , - , - , , - .
6432 4 3
43243 6 63 6
Realizati gura cu cercul trigonometric pentru a justica raspunsul.
2. Folosind formula cos(a - b) = cos a cos b + sin a sin b, deduceti formulele urmatoare:
cos(a + b) = cos a cos b - sin a sin b, sin(a + b) = sin a cos b + cos a sin b, sin(a - b) = sin a cos b - cos a sin b,
sin 2x = 2 sin x cos x, cos 2x = cos2 x - sin2 x = 1 - 2 sin2 x = 2 cos2 x - 1, sin 3x = 3 sin x - 4 sin3 x, cos 3x = 4 cos3 x - 3 cos x,
| sin x | =
1 - cos 2x ,
2
| cos x | =
1 + cos 2x ,
2
sin x = cos( - x),
2 cos x = sin( - x), 2
x+y x-y
sin x + sin y = 2 sin
cos
,
2
2
x-y x+y
sin x - sin y = 2 sin
cos
,
2
2
x+y x-y
cos x + cos y = 2 cos
cos
,
2
2
x-y x+y
cos x - cos y = -2 sin
sin
.
2
2
3.
Daca sin a =
4 5
,
a
(
3 2
,
2)
si
cos
b
=
-
1 3
,
b
(
2
,
),
calculati
sin(a
-
b),
cos(a
+
b),
sin
2a,
cos
3b,
sin
a 2
.
4.
Calculati
cos
7 12
,
sin
10
,
cos
5
.
1
5. Demonstrati ca urmatoarele expresii sunt independente de x:
(a) E = sin2 x cos2 x
1
+
1
;
1-sin2 x(1+cos2 x)
1-cos2 x(1+sin2 x)
(b) E
=
sin(x+y) cos x-sin cos(x+y) cos x+sin
x x
cos(x+y) sin(x+y)
.
6. Vericati identitatile urmatoare, pentru orice x, y R:
(a) cos
x
-
4
cos
4
-
cos
x
+
4
sin
4
=
sin x;
(b) cos2 (x - y) - cos2 (x + y) = sin 2x sin 2y;
(c) sin (x + y) sin (x - y) = sin2 x - sin2 y;
(d)
sin
(2k
+
1)
2
+
x
= (-1)k cos x, k Z;
(e) cos
(2k
+
1)
2
+
x
= (-1)k+1 sin x, k Z.
7. Transformati urmatoarele sume in produse.
(a) S = sin x + sin 3x + sin 5x; (b) S = cos 2x + cos 4x + cos 6x; (c) S = sin x + sin 2x + sin 3x + sin 4x + sin 5x; (d) S = cos x + cos 2x + cos 3x + cos 4x + cos 5x.
Indicatie
pentru
(c),(d):
Calculati
2S
sin
x 2
.
8. Determinati valorile extreme ale functiilor urmatoare.
(a) f : R R, f (x) = sin6 x + cos6 x;
(b) f : R R, f (x) = cos 2x + cos x;
(c)
f
:
[0,
2
]
R,
f (x) = sinm x cosn x, m, n N.
9. Determinati dreptunghiul de arie maxima inscris intr-un cerc dat.
10. Determinati conul circular drept de volum maxim a carui generatoare are lungimea constanta l.
2
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