So ax+60 = 90+180 k.

When x = 30, there is 30a+60=90+ 180k.

So a= 1+6k.

Once again -6

2, let the angle between the last two vectors be a, then we can know that COSA < 0.

That is, COSA = (2te1+7e2) (e1+te2)/(| 2te1+7e2 | * | e1+te2 |).

Because | 2te1+7e2 | *| e1+te2 | >; 0 is constant.

Therefore, (2te1+7e2) (e1+te2) < 0.

Solution 7

In addition, 2te 1+7e2 and e 1+te2 cannot be parallel.

So 2t/ 1 is not equal to 7/t, that is, t is not equal to the root sign of plus or minus 2: 14.