（1）原式=lg2•（lg5+1）+lg5•（lg2+1）-2•lg5•lg2

=lg2+lg5

=1

（2）∵log₇3=a，log₇4=b，

∴log4948=

1

2

log7(3×16)=

1

2

(log73+log716)=

1

2

(log73+2log74)

=

1

2

(a+2b)