6. Известно, что a + b = 9, ab = −12. Найдите значение выражения(a − b)2.

maths is (difficult) than science. this pupil is (bright) in the school . this year i have (many) subject in my timetable than i had last year. he has (funny) nickname. our english language teacher is (good) than their english language teacher. i think literature and history are (interesting) subject.