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A. Sistem Pertidaksamaan Linear

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56<br />

=<br />

⎛ d −b<br />

⎞<br />

⎜ad −bcad−bc⎟ ⎜ ⎟<br />

⎜ −c<br />

a ⎟<br />

⎜ ⎟<br />

⎝ad −bcad−bc⎠ 1 ⎛ d −b⎞<br />

= ⎜<br />

ad − bc −c<br />

a<br />

⎟<br />

⎝ ⎠<br />

Dengan demikian diperoleh:<br />

Jika A =<br />

⎛a b⎞<br />

⎜<br />

c d<br />

⎟<br />

⎝ ⎠ , maka A –1 =<br />

dengan ad – bc ≠ 0<br />

Contoh 2.28<br />

Tentukan invers dari matriks A =<br />

Jawab:<br />

A –1 =<br />

=<br />

A –1 =<br />

1<br />

(3)(2) − (4)(1)<br />

1<br />

2<br />

⎛ 2 −4⎞<br />

⎜<br />

−1<br />

3<br />

⎟<br />

⎝ ⎠<br />

⎛ 1 −2⎞<br />

⎜<br />

1 3<br />

⎟<br />

⎜ ⎜− ⎟<br />

⎝ 2 2⎠<br />

⎛ 2 −4⎞<br />

⎜<br />

−1<br />

3<br />

⎟<br />

⎝ ⎠<br />

1<br />

ad − bc<br />

Matematika SMA/MA Kelas XII Program Bahasa<br />

=<br />

1<br />

det A<br />

⎛3 4⎞<br />

⎜<br />

1 2<br />

⎟<br />

⎝ ⎠ !<br />

⎛ d −b⎞<br />

⎜<br />

−c<br />

a<br />

⎟<br />

⎝ ⎠<br />

⎛ d −b⎞<br />

⎜<br />

−c<br />

a<br />

⎟<br />

⎝ ⎠<br />

Contoh 2.29<br />

Jika X matriks berordo 2 × 2, tentukanlah X dari persamaan berikut ini!<br />

⎛2 1⎞<br />

X ⎜<br />

1 2<br />

⎟<br />

⎝ ⎠ =<br />

⎛ 4 5⎞<br />

⎜<br />

10 11<br />

⎟<br />

⎝ ⎠

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