1. i’m sorry i have broken the glass 2. i haven’t done my homework yet 3. i’ve learnt some new english words 4. i haven’t tidied up my room 5. i haven’t been to berlin 6. i’ve seen some birds in the forest 7. i’ve been there before 8. my classmate has won the competition 9. i’ve been to lots of places 10. i’ve walked my dog already
5b²-(a-2b)²=5b²-(a²-4ab+4b²)=5b²-a²+4ab-4b²=b²-a²+4ab=-a²+4ab+b²