Question

Tolong bantu kerjain, yg b aja ya. kalo yg a udh dikerjain:') jan asal ngerjain kalo cuma buat ngejar poin, saya butuh yg bnr² serius.

Answer 1

cara 1:

*) |a| = √(2²+2²+3²) = √(4+4+9) = √17

*) |b| = √(1²+7²+(-4)²) = √(1+49+16) = √66

*) a+b = (2,2,3)+(1,7,-4) = (3,9,-1)

*) |a+b| = √(3²+9²+(-1)²) = √(9+81+1) = √91

*) |a+b|² = |a|²+|b|²+2|a||b|cosx

(√91)² = (√17)²+(√66)²+2(√17)(√66)cosx

91 = 17+66+2√1122 cosx

8 = 2√1122 cos x

4/√1122 = cosx

x = arc cos (4/√1122) = ±82°

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cara 2

a•b = |a|•|b| cosx

cosx = a•b / |a|•|b|

cosx= (2,2,3)•(1,7,-4)/(√17•√66)

cosx= (2,14,-12)/(√17•√66)

cosx= (2+14-12)/(√17•√66)

cosx= 4/(√17•√66)

cosx= 4/√1122

x = arc cos (4/√1122) = ±82°