Question

若

a

2

=

b

3

=

c

4

，則

3a-2b+5c

-6a-b-3c

=

-

20

27

．

Answer 1

分析：設(shè)

a

2

=

b

3

=

c

4

=k，求出a=2k，b=3k，c=4k，把a、b、c的值代入，即可求出答案．

解答：解：設(shè)

a

2

=

b

3

=

c

4

=k，
則a=2k，b=3k，c=4k，
∴

3a-2b+5c

-6a-b-3c

=

3×2k-2×3k+5×4k

-6×2k-3k-3×4k

=-

20

27

．
故答案為：-

20

27

．

點評：本題考查了比例的性質(zhì)的應(yīng)用，主要考查學(xué)生能否選擇適當?shù)姆椒ㄟM行代入，注意：設(shè)

a

2

=

b

3

=

c

4

=k，求出a=2k，b=3k，c=4k，再進行代入即可．